Computer-based assessment can provide new insights into behavioral processes of task completion that cannot be uncovered by paper-based instruments. Time presents a major characteristic of the task completion process. Psychologically, time on task has 2 different interpretations, suggesting opposing associations with task outcome: Spending more time may be positively related to the outcome as the task is completed more carefully. However, the relation may be negative if working more fluently, and thus faster, reflects higher skill level. Using a dual processing theory framework, the present study argues that the validity of each assumption is dependent on the relative degree of controlled versus routine cognitive processing required by a task, as well as a person's acquired skill. A total of 1,020 persons ages 16 to 65 years participated in the German field test of the Programme for the International Assessment of Adult Competencies. Test takers completed computer-based reading and problem solving tasks. As revealed by linear mixed models, in problem solving, which required controlled processing, the time on task effect was positive and increased with task difficulty. In reading tasks, which required more routine processing, the time on task effect was negative and the more negative, the easier a task was. In problem solving, the positive time on task effect decreased with increasing skill level. In reading, the negative time on task effect increased with increasing skill level. These heterogeneous effects suggest that time on task has no uniform interpretation but is a function of task difficulty and individual skill.There are two fundamental observations on human perfor mance: the result obtained on a task and the time taken (e.g., Ebel, 1953). In educational assessment, the focus is mainly on the task outcome; behavioral processes that led to the result are usually not considered. One reason may be that traditional assessments are paper-based and, hence, are not suitable for collecting behavioral process data at the task level (cf. Scheuermann & Bjomsson, 2009). However, computer-based assessment-besides other ad vantages, such as increased construct validity (e.g., Sireci & Zenisky, 2006) or improved test design (e.g., van der Linden, 2005)-can provide further insights into the task completion pro cess. This is because in computer-based assessment, log file data can be recorded by the assessment system that allows the re searcher to derive theoretically meaningful descriptors of the task completion process. The present study draws on log file data from an international computer-based large-scale assessment to address the question of how time on task is related to the task outcome. As shown in the following, by analyzing the relation of task perfor mance to the time test takers spent on task, we were able to obtain new insights into how the interaction of task and person charac-
